Heat treatment of aluminum alloys



TT FFEIQE.

EARL BLOUGH, OF PARNASUS, PENNSYLVANIA, ASSIGN OR TO ALUMINUM COMPANY OFAMERICA, OF PITTSBURGH, PENNSYLVANIA, A CORPORATION OF PENNSYL- VANIA.

HEAT TREATMENT OF ALUMINUM ALLOYS.

Specification of Letters Patent.

Patented Oct. 25, 1921.

, No Drawing. Application filed November 30, 1917, Serial No. 204,540.Renewed December 28, 1920.

Serial No. 433,691.

T 0 all whom it may concern.

Be it known that I, EARL BLOUGH, a citizen of the United States,residing at Parnasus, in the county of Allegheny and State ofPennsylvania, have invented certain new and useful Improvements in HeatTreatment of Aluminum Alloys, of which the following is a full, clear,and exact description.

This invention relates to the heat treatment of aluminum alloys, and thechief object of the invention is to provide a simple and easily workedmethod of treatment for the purpose of improving the important physicalpropertiesof hardness and tensile strength, especially the latter.

As in the treatment of steel, certain prior processes or methods involveheating the metal and then cooling or quenching it. The presentinvention is based on the discovery that the heat-treatment should beeffected in stages, the first at a rather elevated temperature and thelast at a somewhat lower degree.

In applying my process in the preferred manner, the metal is firstheated to a temperature of about 500 C. or higher, say 575 or more, butin general not above 600. In many cases 520 is satisfactory. Thetemperature may be considerably lower, for ex; ample around 400, but ahigher degree is better. In general, the duration of this heating stageshould be long enough for the metal to reach a state of equilibrium,that is to say, a state in which any internal stresses and strains havebeen relieved and in which there have taken place any thermal reactionsand changes that normally occur at such temperature, as for examplechange in the crystalline structure of the alloy.

The actual time required for this effect is V of course variable withthe nature of the alloy, but ordinarily a period of from two to threehours heating, after the metal has been brought up to the temperature,has been found suflicient. If such a period does not give the desiredresults in any specific instance longer periods may be tried. Theheating is now continued (without intermediate rolling, stamping,drawing or other working) at a lower temperature, which may be betweenabout 100 and about 200. Good results are secured at 100, and thistemperature is advantageous because of the convenience with which it canbe obtained and maintained by means of boiling water. \Vith any materialadvantage in temperatures much above 200, say 250, it has been observedthat the elongation is apt to be impaired and the improvement in tensilestrength diminished. A time of two hours for the second heating is amplefor most purposes, but it may be prolonged beyond that. I have not,however, observed continuing the second heatin longer than abouttwentyfour hours. fnstead of continuing the second heating stage it maybe maintained merely long enough for the lower temperature to becomeuniform throughout the metal, after which the temperature can be raised,say to between 150 and 200, about, and kept there until the resultsdesired are attained.

The metal can now be cooled, quickly or slowly, whereupon it will befound that its tensile strength has been very remarkably increased. Noris it necessary to store the metal, or allow it to rest, for a timeafter cooling, before it is used. On the contrary, the metal can at oncebe put to any use for which it is suitable. In fact, with a finalheating stage or step lasting no more than twenty-four hours the tensilestrength has been found to be superior to that resulting from four daysstoring after cooling followin a single heating.

IVIy process is applicable to a great variety of aluminum-copper alloys,and to aluminum-copper alloys containing also one or more of othermetals, for example, zinc, magnesium, iron, calcium, and silicon. It isparticularly effective with alloys in which the copper content does notexceed about ten per cent.

The temperatures referred to in the foregoing description and in theappended claims are all measured on the Centigrade scale.

I claim 2-- '1. In a method of heat-treating aluminum alloy of the kinddescribed to improve certain of its physical properties, especiallytensile strength, the steps comprising subjecting the said alloy to heatat a tempera ture above about 400 C., and, without working the alloy,subjecting it for a period of time to heat at a lower temperature.

2. In a method of heat-treating aluminum alloy of the kind described, toimprovecertain of its physical properties, especially tensile strength,the steps comprising subjecting the alloy to heat at a temperature ofabove about 400 0., and, without working the alloy, subjecting it for aperiod of time to heat at a temperature not less than about 100 O.

. 3. In a method of heat-treating aluminum alloy of the kind described,to improve certain of its physical properties, especially tensilestrength,the steps comprising subjectheating for a period of time at atemperature of not less than about 100 C.

5. In a method of'heat-treating aluminum alloy of the kind described, toimprove certain of its physical properties, especially tensile strength,the steps comprising subjecting the alloy to heat at a temperature aboveabout 400 C., and, without working the alloy, subjecting it to furtherheating at a lower temperature for a period of not less than about twohours.

6. In a method of heat-treating aluminum alloy of the kind described, toimprove certain of its physical properties, especially tensile strength,the steps comprising sub-- jecting the alloy to heat at a temperatureabove about 400 C., and, without working the alloy, subjecting it tofurther heating at a temperature of not less than about 100 0., for aperiod of not less than about two hours.

7. In a method of heat-treating aluminum alloy of the kind described, toimprove certain of 1ts physlcal properties, especially tens le strength,the steps comprising subecting the alloy to heat at a temperature of notless than about 500 CT, and, without working the alloy, subjecting it tofurther heatlng at a lower temperature for a period of not less thanabout two hours. I

8. In a method of heat-treating aluminum alloy of the kind described, toimprove certain of its physical properties, especially tens le strength,the steps comprising subecting the alloy to heat at a temperature notless than about 500 C., and, without working the alloy, subjecting it-tofurther heating at a temperature of not less than about 100 C., foraperiod of not less than about two hours.

9. In a method of heat-treating aluminum alloy of the kind described, toimprove certain of 1ts physical properties, especially tensile strength,the steps comprising subjecting the alloy to heat at a temperature aboveabout 400 C., then, without working jecting the alloy to heat at atemperature above about 500 C., then, without working the alloy, subjectit to heat at a temperature above about 100 0., then without working thealloy subjecting it for a period of time to heat at a higher temperaturethen that used in said second step, but below 300 C.

11. In a method of heat-treating aluminum alloy of the kind described,to improve certain of its physical properties, especially tensilestrength, the steps comprising subjecting the alloy to heat at anelevated temperature, then, without working the alloy, lowering itstemperature materially; then, without working the alloy, raising itstemperature and maintaining it for-a period of time at a temperaturematerially higher than that to which the temperature had been soreduced, but lower than that atwhich the alloy was subjected in suchfirst step.

12. In a method of heat-treating aluminum alloy of the kind described,to improve certain of its physical properties, especially tensilestrength, the steps comprising subjecting the alloy to heat at anelevated temperature,-then, without working the alloy, lowering itstemperature materially, then, without working the alloy, raising itstemperature and maintaining it for not less than two hours at atemperature materially higher than that to which the temperature hadbeen lowered, but lower than that at which the alloy was treated in thefirst step.

13. In a method of heat-treating aluminum alloy of the kind described,to improve certain of its physical properties, especially tensilestrength, subjecting the alloy to heat in a plurality of stages withoutintermedlate working, at least two of the stages each lasting for amaterial period of tlme; the first at a temperature exceeding 400 C.,and another at a temperature more than 200 C. lower than the first. I

14. In a method of heat-treating aluminum alloy of the kind described,to improve certain of its physical properties, especially tensilestreigth, subjecting the alloy to heat in a plurality of stages withoutintermediate working, at least two of the stages each lasting for asufficient length of time to establish the internal structure of thealloy in an approximately stable state at that temperature, thetemperature in the first of said stages exceeding 400 (3., and thetemperature in a subsequent one of said stages being more than 200 C.lower than that in the first stage.

15. In a method of heat-treating aluminum alloy of the kind described,to improve certain of its physical properties, especially tensilestrength, subjecting the alloy to heat in a plurality of stages withoutintermediate working, at least two of the stages each lasting for asufiicient length of time to establish the internal structure of thealloy in an approximately stable state at that temperature, thetemperature in the first stage exceeding 400 (7., and the temperature inanother of said stages being between 100 C. and 250 C, approximately.

16. In a method of heattreating aluminum alloy of the kind described, toimprove certain of its physical properties, especially tensile strength.subjecting the alloy to heat at an elevated temperature until theinternal stresses existing have been relieved and the thermal reactionsand changes that normally occur at such a temperature have taken place,and thereafter subjecting the alloy, without intermediate working, toheat at a lower temperature for time.

I 17. In a method of heat-treating aluminum alloy of the kind described,to improve certain of its physical properties, especially tensilestrength, subjecting the alloy to heat at an elevated temperature untilthe internal stresses existing have been relieved and the thermalreactions and changes that normally occur at such a temperature havetaken place, and thereafter subjecting the alloy, without intermediateworking. to heat at a lower temperature above about 100 C. for amaterial period of time.

18. In a method of heat-treating aluminum alloy of the kind described,to improve certain of its physical properties. especially tensilestrength, subjecting the alloy to heat at an elevated temperature untilthe internal stresses existing have been relieved and the thermalreactions and changes that normally occur at such a temperature havetaken place, and thereafter subjecting the alloy, without intermediateworking, to heat at a lower temperature for not less than about twohours.

19. In a method of heat-treating aluminum alloy of the kind described,to improve certain of its physical properties, especially tensilestrength, subjecting the alloy to heat at an elevated temperature untilthe internal stresses existing have been relieved and the thermalreactions and changes that normally occur at such a temperature havetaken place, and thereafter subjecting the alloy,

without intermediate working, to heat at a a material period of lowertemperature between about 100 C and 300 C., for not less than about twohours.

20. In a method of heat-treating aluminum alloy of the kind described,toimprove certain of its physical properties, especially tensilestrength, subjecting the alloy to heat at a temperature of above 400 C.,and, without working the alloy, quenching it in boiling water; then,without intermediate working, heating it in boiling water for a materialperiod of time.

21. In a method of heat-treating aluminum alloy of the kind described,to improve certain of its physical properties, especially tensilestrength, subjecting the alloy to heat at a temperature of over 400 C.,and, without working the alloy, quenching it in boil ing water; then,without intermediate working, heating it in boiling water for not lessthan about two hours.

22. In a method of heat-treating aluminum alloy of the kind described,to improve certain of its physical properties, especially tensilestrength, subjecting the alloy to heat at a temperature of over 500 C.,and, without working the alloy, quenching it in boiling water; then,without intermediate working, heating it in boiling water for a materialperiod of time.

23. In a method of heat-treating aluminum alloy of the kind described,to improve certain ofits physical properties, especially tensilestrength, subjecting the alloy to heat at a temperature of over 500 0.,and, without working the alloy, quenching it in boiling water; then,without intermediate working, heating it in boiling water for not lessthan about two hours.

'24. In a method of heat-treating aluminum alloy of the kind described,to improve certain of its physical properties, especially tensilestrength, subjecting the alloy to heat at a temperature of over 400 C.,and, without working the alloy, quenching it in boiling water; then,without intermediate working, subjecting it'to a further heating at atemperature betweenl about 100 C. and 300 (1., for a material period oftime. e

25. In a method of heat-treating aluminum alloy of the kind described,to improve certain of its physical properties, especially tensilestrength, subjecting the alloy to heat at a temperature of over 500 C,and, without working the alloy, quenching it in boiling water; then,without intermediate Working, subjecting it to a further heating at atemperature above about 100 C, for not less than about two hours.

In testimony whereof I hereunt affix my signature.

EARL BLOUGH.

